Providing an Open API and SPI

Non-invasive integration is one of the goals of the ESG pattern. This is important when you do not have control of the other systems. But it means that you are taking on the responsibility of implementing the integrations that adapt the other systems to your system. This is only manageable for a limited number of systems.If you are implementing your own SaaS product, then the number of external systems that want to integrate with your system can be limitless. In this case, the only manageable solution is to provide your own open interface and make the external systems responsible for integrating with your system.Open interfaces expose your external domain model to the outside world. They act as a façade to hide the inner workings and provide strong backward compatibility guarantees. They simplify the process of integrating with your system and enable external systems to take on the responsibility for connecting to your system and transforming between...